sFLCs may be a useful additional marker to monitor WM. Their short serum half-life and the large clinical range provide a sensitive marker for assessment of response to treatment.
Leleu et al.  studied the use of sFLCs to monitor response to treatment in 48 WM patients (untreated [n=20] or relapse and/or refractory [n=28]), participating in a trial of bortezomib and rituximab treatment. The proportion of patients who demonstrated a response to therapy was higher using sFLC analysis (79%, defined as a ≥50% decrease in iFLC from baseline) than monoclonal protein quantification by SPE (60%). Similar results were obtained when the difference between the iFLC and uninvolved (uFLC) sFLC concentrations (dFLC) was used as an alternative measure of sFLC response (κ-statistic 0.89). In addition, the time to response was shorter when assessed using iFLC compared to the monoclonal protein response (2.1 vs 3.7 months, p=0.05) . There was a significant correlation of progression as defined by iFLC or SPE criteria (a >25% increase from maximum response), with 81% of patients showing concordance of both markers (κ-statistic: 0.63). The median time to progression (TTP) was shorter as measured by iFLC than by following SPE criteria (13.7 vs. 18.9 months, respectively). The authors concluded that iFLC was a sensitive marker for the early determination of response and progression in WM.
An update of the consensus panel criteria for the assessment of clinical response in patients with WM stated that whilst there were insufficient data to incorporate sFLC assessments into the revised criteria, further prospective evaluation was encouraged . Similarly, British guidelines also highlight the potential utility of sFLC measurements for the assessment of response in WM .